docs: def _progressbar(self, msg, iter_num):
          """Display a progress bar with current loss.
  
          Parameters
          ----------
          msg : str
              Message to print alongside the progress bar
  
          iter_num : int
              Iteration number.
              Progress is only printed if this is a multiple of
              `self.display_progress`.
  
          """
          if self.display_progress and \
                                  (iter_num + 1) % self.display_progress == 0:
              sys.stderr.write('\r')
              sys.stderr.write("Iteration {}: {}".format(iter_num + 1, msg))
              sys.stderr.flush()